The Araucaria Project: The distance to the Fornax Dwarf Galaxy from near-infrared photometry of RR Lyrae stars

TL;DR

This study uses near-infrared photometry of RR Lyrae stars to accurately determine the distance to the Fornax Dwarf Galaxy, achieving high precision and confirming the method's robustness for galactic and extragalactic distance measurements.

Contribution

It provides a new, precise distance measurement to the Fornax Dwarf Galaxy using NIR RR Lyrae stars and demonstrates the method's reduced sensitivity to metallicity and reddening effects.

Findings

Distance modulus of 20.818 mag with 5% precision

Agreement with other independent distance measurements

Reduced impact of metallicity and reddening in NIR

Abstract

We have obtained single-phase near-infrared (NIR) magnitudes in the J- and K-bands for 77 RR Lyrae (RRL) stars in the Fornax Dwarf Spheroidal Galaxy. We have used different theoretical and empirical NIR period-luminosity-metallicity calibrations for RRL stars to derive their absolute magnitudes, and found a true, reddening-corrected distance modulus of 20.818 +/- 0.015 (statistical) +/- 0.116 (systematic) mag. This value is in excellent agreement with the results obtained within the Araucaria Project from the NIR photometry of red clump stars (20.858 +/- 0.013 mag), the tip of the red giant branch (20.84 +/- 0.04 +/- 0.14 mag), as well as with other independent distance determinations to this galaxy. The effect of metallicity and reddening is substantially reduced in the NIR domain, making this method a robust tool for accurate distance determination at the 5 percent level. This precision is expected to reach the level of 3 percent once the zero points of distance calibrations are refined thanks to the Gaia mission. NIR period-luminosity-metallicity relations of RRL stars are particularly useful for distance determinations to galaxies and globular clusters up to 300 kpc, that lack young standard candles, like Cepheids.